I'm trying to get my head around DDD but I'm stuck. This is how I setup my project:
Data Access Layer
-Entity models that map to the db
-Db connection stuff
-Repositories implementations
Domain Layer
-Models that represent the DAL entity models
-Repositories interfaces
Application Layer
-MVC application that uses Domain models
The first problem I see here is that the Domain models are exactly the same as the Entity models, and I have a serious problem with this: the entity models obviously have validation configured into them, things like "max length", "nullable", "required", etc. Now, to conform to what I understand is DDD, I can't directly use these models anywhere, except the DAL, so I created my domain layer. In the domain layer, I have all these validation rules duplicated for UI validation, and what's even worse, is that if I need to change a rule, I will have to change it in two places: the DAL and the Domain.
Example:
User Entity in DAL
Name (required)
Last name (required)
Email (required, maxlen 120)
Username (required, maxlen 120)
User Domain Model
Name (required)
Last name (required)
Email (required, maxlen 120)
Username (required, maxlen 120)
Another thing that I find very weird is that the repositories organization in this architecture. Following what I read, I created a GenericRepository interface, and a UserRepository interface, which inherits the GenericRepository, all in the Domain layer. I implemented the GenericRepository in the DAL, and the implementation creates a DAO for the type of the entity used to create the repository. So far, so good.
Then, I proceeded to implement the UserRepository, and here I have another problem: the UserRepository interface expects the Domain User model, and when I try to implement the interface in the DAL, I need to implement it using the Domain User model, which causes the DAO to be created for a Domain model, not a DAL model, and this doesn't make any sense. The only to fix it would be to reference the DAL in the Domain layer, which is wrong.
Domain Layer:
public interface IGenericRepository<TEntity>
{
TEntity FindById(TKey id);
}
public interface IUserRepository : IGenericRepository<Domain.User>
{
Task<User> FindByUserNameAsync(string userName);
}
DAL:
public abstract class GenericRepository<TEntity> : IGenericRepository<TEntity>
{
protected DbContext ctx;
protected DAO<Entity> dao;
public GenericRepository(DbContext context)
{
ctx = context;
dao= ctx.Dao<TEntity>();
}
public virtual TEntity FindById(TKey id)
{
return dao.Find(id);
}
}
public class UserRepository : GenericRepository<Domain.Models.User>, IUserRepository
{
public UserRepository(DbContext context)
: base(context)
{
// THIS WILL CREATE A DAO FOR A DOMAIN MODEL
}
// rest of code...
}
Can anybody shed a light on what I'm missing from DDD?
